The invention relates to a process for cooling a device for charging a shaft furnace. A device for charging a shaft furnace of the type considered in the invention comprises in particular a support casing mounted on the head of the furnace, loading equipment suspended in a rotatable manner on the support casing, and at least one cooling circuit supported by rotatable charging equipment and fed by a ring-shaped rotating connection device.
Such a charging device is described, for example, in Luxembourg patent application LU 80112. The charging equipment comprises a charging trough suspended in a suspension cage, which is itself suspended in the support casing, in such a way as to be set in rotation, and which is traversed by a central feed channel for the trough. This suspension cage also forms a protection screen around the feed channel, which protects the implementation devices located in the support casing, and in particular against the radiation of heat from the interior of the shaft furnace. The suspension cage for the distribution trough is provided with a cooling circuit. This is supplied by a cooling liquid by means of a ring-shaped rotating connection device, located around the feed channel for the trough. The connection device comprises a rotating shell, which is carried by the suspension cage, and a fixed yoke. This yoke is carried by the support casing, and the rotating shell is arranged with a degree of play in the fixed yoke. Two ring-shaped throats located above are provided in the fixed yoke, in such a way as to juxtapose the outer cylindrical surface of the rotating shell. A number of connection pipes for the cooling circuit define the location of openings in the outer cylindrical surface of the rotating shell opposite the two throats. Sealing devices, which are mounted along the length of the two edges of each throat, are supported on the outer cylindrical surface of the rotating shell, with the aim of ensuring the sealing effect between the rotating shell and the fixed yoke. It has been found that this type of rotating connection, which in particular requires a relatively low amount of play between the rotating shell and the fixed yoke so as to guarantee the seal, is hardly well-suited for a charging device for a shaft furnace. In a shaft furnace, the rotating shell and the fixed yoke in fact risk suffering from very different thermal expansion, as well as mechanical stresses, which rapidly lead to the blockage of the connection with low functional play. in addition to this, in the environment of a shaft furnace, it must always be assumed that there will be substantial volumes of dust present. This dust will inevitably penetrate between the rotating shell and the fixed yoke, where it risks incurring a blockage of the rotating connection or of destroying the sealing devices. It must also be borne in mind that the sealing devices are in contact with a shell which is quite hot, which is hardly favourable to them. It is therefore not surprising that a rotating connection system of this type has never in practice been applied to a shaft furnace.
Accordingly, in 1982, the company of Paul Wurth S. A. proposed a cooling arrangement for a charging installation of a blast furnace without sealing devices. This cooling arrangement, which is described in detail in patent application EP 0 116 142, has been installed in numerous blast furnace charging installations throughout the world. It is characterised by a ring-shaped trough, which is supported by a shell above the rotating cage, which is gravity-fed with cooling water. For this purpose, a cooling water feed duct is integrated in the support casing and features, above the ring-shaped trough, at least one opening allowing for the gravity circulation of the cooling water in the ring-shaped trough in rotation with the suspension cage. The latter is connected to several cooling coils which equip the rotating cage. These coils are outlet ducts, which empty into a ring-shaped collector supported by the lower edge of the support casing. The water consequently flows by gravity, starting from a fixed-position feed pipe in rotation, into the ring-shaped trough in rotation, passing by gravity through the cooling coils mounted on the rotating cage, and then is collected in the lower fixed-position collector, and evacuated on the outside of the support casing. This water circulation system is monitored by level sensors connected to the ring-shaped trough and the lower collector. In the ring-shaped trough, the level is adjusted in such a way as to be constantly between a minimum level and a maximum level. If the level drops as far as the minimum level, the feed outlet of the ring-shaped trough is increased, so as to guarantee the appropriate feed to the coils. If the level rises as far as the maximum level, the feed outlet of the ring-shaped trough will be reduced, so as to avoid overflow from the ring-shaped trough.
A disadvantage of the 1982 cooling arrangement is that the gases from the blast furnace come in contact with the cooling water in the ring-shaped trough. Because these blast furnace gases are heavily laden with dust, substantial quantities of dust pass into the cooling water. This dust forms sludges in the ring-shaped trough, which pass into the cooling coils and risk blocking them. In this context it is appropriate to note, inter alia, that the pressure available to cause the water to pass through the coils is determined essentially by the height differential between the ring-shaped trough and the lower collector.
The present invention, such as defined in Claim One, achieves a significant reduction of the risk of penetration of the dust into the cooling circuit.
The process according to the invention relates more specifically to a device for charging a shaft furnace, comprising: a support casing mounted on the head of the furnace, charging equipment suspended in rotatable fashion in the support casing, a cooling circuit supported by the rotating charging equipment in such a way as to induce rotation in the latter, as well as a ring-shaped rotating connection device, this connection device comprising a fixed part and a rotating part, capable of turning with the rotating charging equipment, the rotating part being separated from the fixed part by means of a ring-shaped separation gap so as to allow for relative rotation. In a known manner, the fixed part of the connection device is fed with a cooling liquid, which passes into the rotating part of the connection device where it feeds the cooling circuit, so as then to be evacuated at the outlet of the cooling circuit on the outside of the support casing. By contrast with arrangements of the state of the art, however, there is no attempt to ensure the perfect sealing of the turning connection, such as provided for, for example, under patent application LU 80112, nor to avoid leaks from the turning connection by means of a system of level sensors, such as is provided for, for example, in patent application EP 0116142. In fact, according to the invention, the feed of a cooling liquid of the turning connection is effected in such a way that a leakage outlet passes through the ring-shaped separation gap, so as to form therein a liquid joint, this leakage outlet being collected and evacuated outside the support casing without passing through the cooling circuit. In other words, the cooling liquid is used to plug the ring-shaped separation gap, which must exist between the rotating and fixed parts of the rotating connection so as to allow for rotation to take place, and which allows for the interior of the cooling circuit to be in communication with the furnace surroundings. The leak rate, which has formed this liquid joint, is then collected and evacuated directly outside the support casing, without passing through the cooling circuit. The result of this is that the dust sludges formed in the gap no longer pass through the cooling circuit and therefore do not incur the risk of blockage.
In most cases, it will be of advantage to provide the connection device with elements which are capable of creating an additional charge loss at the level of the ring-shaped separation gap, in such a way that the feed pressure of the cooling liquid may be perceptibly higher than the counter-pressure which prevails in the support casing, without generating any too substantial leak rate. In other words, the invention allows for the first time for a cooling circuit for rotating charging equipment to be fed with suppression capability. This not being further limited from the point of view of feed pressure, it is plainly possible to create cooling circuits of higher performance. It will also be appreciated that the leak rate which passes through those elements which are prone to incur a loss in supplementary pressure (such as fittings, elastomer joints, labyrinth joints, etc.) guarantees a cooling effect, a certain degree of lubrication, and the constant cleaning of these elements, which undoubtedly has a beneficial effect on their service life.
In a first embodiment, the connection device consists of a ring-shaped block carried by the support casing, and delimited by two cylindrical surfaces, as well as a ring-shaped channel, carried by the loading equipment and delimited by two cylindrical surfaces. The ring-shaped block, fixed in rotation, penetrates into the ring-shaped channel in such a way that the juxtaposed cylindrical surfaces delimit two ring-shaped spaces which form part of said ring-shaped separation gap. The ring-shaped channel is provided to advantage with overflow apertures connected to the pipes for evacuating the leak rate. So as to create an additional loss of charge, which reduces the leak rate when the cooling water feed pressure is increased, provision is made between the two juxtaposed cylindrical surfaces, below the overflow apertures, for elastomer ring-shaped joints, such as lip joints. The ring-shaped block, which is carried by the support casing, comprises to advantage a number of passages which allow for communication between the two ring-shaped spaces, in such a way that there is pressure equilibrium between the two ring-shaped spaces.
According to a second embodiment, the connection device comprises a ring, provided with a ring-shaped front surface fixed in rotation, as well as a ring-shaped channel of one piece wit the charging equipment. The ring is located in the ring-shaped channel in such a way that its front ring-shaped surface is positioned opposite a ring-shaped surface in the ring-shaped channel, a ring-shaped gap separating the two juxtaposed ring-shaped surfaces. A set of fittings is then arranged between the two ring-shaped surfaces, so as to create an additional loss of charge in said separation ring. The ring is to advantage mounted in such a way that it can undergo translation parallel to the axis of rotation, in order for it to be able to exercise a certain amount of pressure on the set of fittings. In a first embodiment, the ring is supported by compensators, in such a way as to be able to undergo slight displacement parallel to the axis of rotation. In a second embodiment, the ring is connected with the aid of a sliding connection to a fixed ring-shaped block, in such a way as to be able to slide parallel to the axis of rotation.
According to another embodiment, the ring-shaped separation gap forms at least one labyrinth joint. In this case, the connection device comprises to advantage a ring-shaped block which is carried by the support casing and delimit laterally by two staged ring-shaped surfaces, as well as a ring-shaped channel, carried by the charging equipment and delimited laterally by two staged ring-shaped surfaces, in a complementary manner. The ring-shaped block then penetrates into the ring-shaped channel in such a way that the two juxtaposed staged surfaces interact so as to form a labyrinth joint, which forms part of said ring-shaped separation gap. As already described previously, the ring-shaped channel is provided to advantage with overflow apertures connected to the pipes for evacuating the leak rate, and located above the labyrinth joint, and the ring-shaped block, carried by the support casing, comprises to advantage passages which allow for communication between the two ring-shaped spaces.